https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101770
Bug ID: 101770
Summary: -Wmaybe-uninitialized false alarm with only locals in
GNU diffutils
Product: gcc
Version: 11.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: eggert at cs dot ucla.edu
Target Milestone: ---
Created attachment 51256
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51256&action=edit
False alarm with gcc -O2 -Wmaybe-uninitialized and only locals
I found this problem while compiling sdiff.c from GNU diffutils. The attached
is is a simplified version. It appears to be distinct from GCC bug 101768 since
it involves only local variables.
Compile it this way:
gcc -O2 -Wmaybe-uninitialized -S w.i
The output is:
w.i: In function ‘edit’:
w.i:50:18: warning: ‘cmd1’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
50 | return !cmd1;
| ^~~~~
This is a false alarm, because line 50 can be reached only if cmd0=='e', and if
cmd0=='e' then the previous switch statement (inside the while loop - line 27)
guarantees that cmd1 has been initialized.
I briefly tried to simplify the example further, but failed. For example, if I
remove line 16 ("case '2':") the false alarm goes away.
This is with gcc (GCC) 11.2.1 20210728 (Red Hat 11.2.1-1) on x86-64.
